Indacaterol is the international nonproprietary name of the compound (R)-5-[2-[(5,6-diethyl-2,3-dihydro-1H-inden-2-yl)amino]-1-hydroxyethyl]-8-hydroxyquinolin-2(1H)-one, having the following formula:

Indacaterol is a drug acting as selective agonist of beta-2 receptors and is recommended in the bronchospasm and in other bronchial pathological conditions such as bronchial asthma and chronic obstructive pulmonary disease.
Some synthesis of the indacaterol are known which make use of 4,5-diethyl-1H-inden-2-yl-amine with the following formula

or N-substituted derivatives thereof, in particular the N-benzyl derivative, as key intermediates. Said intermediates are usually produced starting from the indanamine after protection of the amine group. For example, WO03/076387 describes the preparation of 4,5-diethyl-1H-inden-2-yl-amine starting from the indanamine protected with trifluoroacetyl, by means of two consecutive Friedel-Crafts reactions, each of them followed by the reduction of the introduced ketone group. The above indicated process has the drawback of requiring the isolation and purification of the compounds obtained after each individual reaction step, thus resulting in a process complexity related to the several isolations of the intermediates and, obviously, in a yield loss.
Moreover, the preparation of the derivative wherein R is a benzyl group is described starting from the 4,5-diethyl-1H-inden-2-yl-amine, whose amine group is reacted with benzyl chloride and then subjected to reduction, according to the following scheme:

As it can be noted, the preparation of the benzyl derivative reported above requires two additional reaction steps, which affect the economy of the synthesis and determines higher costs, in particular in the case of industrial production.
WO 00/75114 describes the preparation of 4,5-diethyl-1H-inden-2-yl-amine starting from diethylbenzene; the process results in very low yields and, in addition, the starting compound (diethylbenzene) is particularly expensive. These drawbacks make the process described in WO00/75114 of no industrial interest.
Therefore, there is the need of finding a synthesis of the compounds of formula (I) which is of simple realization and does not require complex isolation and purification steps of the intermediates.